When performing scale predictions at different temperature and pressure points in ScaleChem, users can choose whether to remove solids that form at each step or carry them forward to subsequent calculation points.
This choice is controlled by the “Drop solids” checkbox.
Disclaimer
The user interface, calculations, and results displayed in this article are from OLI Studio: ScaleChem Version 12.5. Other software versions may appear different due to continual developments to the software.
1. Local Scale Precipitation (“Drop Solids” Selected)
When the “Drop solids” box is selected, any precipitated scale at a given calculation point is removed from the system before proceeding to the next step.
In ScaleChem, the “Drop solids” box can be found in the “Conditions” tab of a “Scale Scenarios” calculation and in the “Inflow Specs” or “Conditions” tab in “Facilities”.
(a)
(b)
Figure 1. The "Drop Solids" box available in the "Conditions" tab of (a) a "Scale Scenario" calculation and (b) a "Facilities" calculation in OLI Studio: ScaleChem.
This setting assumes that:
- Kinetics are favorable for scale formation.
- Thermodynamic equilibrium is achieved locally.
- The scale that can form does form and deposits at that location.
As a result, these solids are not available at subsequent calculation points.
This configuration represents local scale precipitation.
An example is a manifold mixing case where incompatible brines (for example, one rich in Ba²⁺ and another in SO₄²⁻) combine. The chart below shows the mass of BaSO₄ predicted to precipitate as a result of the mixing at that specific point.
Figure 2. Example of local scale precipitation in a manifold mixing case (Ba²⁺/SO₄²⁻ incompatibility).
2. Cumulative Scale Precipitation (“Drop Solids” Unselected)
If the “Drop solids” box is not selected, the solids that can form at one calculation point are carried through to the next point.
The resulting output is a cumulative scale precipitation curve.
This approach assumes that:
- Kinetics are not favorable, and the supersaturated solution does not have enough time to precipitate scale, and/or
- Scale forms but does not adhere at that point and is instead transported further downstream.
This configuration represents the worst-case scenario, showing the total potential for scale accumulation across the system and it reflects the overall system behavior rather than local equilibrium.
This approach is particularly useful for assessing:
- Potential re-dissolution of scale downstream.
- The effect of saturation ratio (SR) changes on overall scale risk, rather than only at specific points.
Figure 3. Example of cumulative scale precipitation (same mixing case, with solids carried through downstream of each mixing point).
3. Practical Use and Recommendations
Both local and cumulative scale predictions provide valuable and complementary insights.
In ScaleChem, users can easily generate both types of results by toggling the “Drop solids” checkbox on or off.
In ScaleChem, the “Drop solids” box can be found in the “Conditions” tab of a “Scale Scenarios” calculation and in the “Inflow Specs” or “Conditions” tab in “Facilities”.
Recommended workflow:
- Run cumulative scale predictions first – to identify the worst-case scenario across the system.
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Then run local predictions – when:
- There is confidence that scale will form and deposit at specific points, or
- The impact of a temperature/pressure change or a mixing point needs to be analyzed in detail.
4. Scale Removal Options in Studio vs Flowsheet
In OLI Studio, the “Drop solids” option applies globally — users can either:
- Remove all solids at each calculation point, or
- Retain all solids throughout the entire profile.
In contrast, OLI Flowsheet allows more flexibility.
Users can specify partial solid removal, choosing to drop only a percentage of the predicted solids while carrying forward the remaining fraction. This can be achieved by adding “Solids in liquid” entrainment in separator outlet streams.
This feature enables more realistic modeling of partial deposition and transport processes in complex systems.